Peak to Average Power Ratio (PAPR) is an important metric for the waveform defined by a wireless standard as it directly impacts transmitter power efficiency and ultimately the battery life of a mobile terminal and/or the coverage area of a cellular base station. At the same time, orthogonal frequency division multiple access (OFDMA) has come to be viewed as a superior modulation scheme. Particularly for the cellular downlink, OFDMA is effectively replacing CDMA in newer broadband wireless standards. However, orthogonal frequency division multiplexing (OFDM) and OFDMA are also known to exhibit a large PAPR, which, although reasonable for the downlink signal from the base station, can be problematic for the uplink signal from the mobile terminal.
WiMAX (i.e., the Worldwide interoperability for Microwave Access), as currently defined by IEEE (Institute of Electrical and Electronics Engineers) 802.16-series specification, uses OFDMA in the uplink due to its generally outstanding properties and in order to simplify the overall standard by maintaining similarity with the downlink signal. In contrast, the long term evolution (LTE) effort in the third generation partnership project, known as 3GPP, is contemplating the use of SC-FDMA (Single Carrier-Frequency Division Multiple Access) in the uplink while maintaining a choice of OFDMA for the downlink. The justification for choosing SC-FDMA over OFDMA in the LTE uplink was due to the PAPR issue.
The split between the WiMAX and the 3GPP/LTE camps over the best form of uplink modulation has stirred some debate within the wireless community. This debate raises the uncertainty about the direction a future release of the WiMAX standard may take. However, since the relative superiority of one scheme over the other is a direct function of the scenario being considered, there is no clear resolution of this issue.